The sensor itself works in a swipe manner, which means that you
would need to swipe the entire pad of your finger, from base to
tip, across the home key to register your fingerprint properly.
Also, you would need to keep your finger flat against the home
key and swipe at a moderate speed or else it won’t recognise
your fingerprint. The fingerprint sensor is sensitive to
moisture, as well. So, don’t try to use it with wet fingers
because it will, literally, give you an error and tell you to
dry your fingers first.
Swipe sensors have a bad reputation for being finicky, but we shall see. (Don’t miss the comments on this article; they’re a hoot.)